There exists a requirement in many fluidic systems for variable linear resistors. For example, variable linear resistors are needed to set the scale factor in linear scaler. Many ways exist to vary flow resistance. The most common one is the use of a needle valve. However, the resistance of a needle valve is nonlinear, and this limits its usefulness in fluidic control systems.
One attempt to design a variable linear resistor is described in "The Design of a Flueric Linear Resistor," by George Mon, United States Army, Harry Diamond Laboratories report #HDL-R-RCA-76-6, published June, 1975. In it the principle of a fully developed flow through a rectangular channel is used in which the flow resistance is linearly related to the pressure drop (in the design of a linear resistor). The resistor is made up of a number of discrete resistor laminates. By stacking these rectangular channel laminates in parallel, the resistance of the resistor can be changed. However, this design does not have a continuous variation of the resistance, due to the fact that the resistor is constructed out of discrete resistor laminates. As a result, it is very difficult to design a resistor to have an exact value and its value cannot be changed while in use.
The variable linear resistor of the present invention is presented to overcome the shortcomings of the needle valve and the laminate type resistor. The variable linear resistor of the present invention has a linear relationship between the flow rate and the pressure drop and its value can be precisely set in a manner similar to that of a needle valve.